Cleaning process

Abstract: A method for post-cleaning finish drying is provided, by which finish drying of industrial parts can be conducted without leaving residues or corroding the cleaned material. In this method, finish drying can be performed without the use of flon being a cause of destruction of the ozono-sphere. Preferably, a cleaned material is dipped (rinsed) in a low molecular weight siloxane having a content of organic compounds, such as dodecamethylpentasiloxane, of less than 0.01 % by weight, taken out and dried. Also, preferably, the material rinsed with the low molecular weight siloxane is subjected to a vapor cleaning using a perfluorocarbon compound.

Description: Background of The Invention Field of The Invention The present invention relates to a method for finish drying to be conducted in a final step subsequent to cleaning of industrial parts, in which finish drying of industrial parts, e.g., optical and molded parts composed of glass or plastic, metallic parts, ceramic parts and electronic parts, upon cleaning can be performed without causing the parts to have stain and residue, so that the industrial parts having undergone the finish drying can be directly fed to surface treatment, e.g., formation of a vacuum deposition film on the surface of the parts. In particular, the present invention is concerned with the method in which finish drying can be accomplished without the use of flon, the reduction of the use thereof being worldwide demanded in recent years. Discussion of Related Art Generally, for industrial parts, such as optical, molded and electronic parts, finish drying is performed after precision cleaning thereof for defatting. This post-cleaning finish drying has been performed by the vapor drying using 1,1,2-trichloro-1,2,2-trifluoroethane (flon 113). The flon 113 has predominantly been used because it is incombustible, has low toxicity to organisms, can rapidly be dried and exhibits selective dissolving power (fats and oils are effectively dissolved while polymeric materials, such as plastic and rubber, are not corroded). However, flon 113 (and other perhaloethanes) are so chemically stable that the life thereof in the troposphere is long. Thus, flon 113 is diffused into the stratosphere, where it is decomposed by sunbeams to produce halogen radicals. The halogen radicals incur chain reaction with ozone to thereby destroy the ozonosphere. Therefore, the reduction of the use of flon 113 is strongly demanded. In accordance with the demand for the reduction of the use of flon 113 for the protection of the ozonosphere, proposals have been made to carry out finish drying by the use of a large variety of solvent mixtures and azeotropic compositions. For example, Japanese Unexamined Patent Application Publication No.1-318094 (1989) discloses a solvent composed of a mixture of flon 113, isopropyl alcohol and methyl ethyl ketone. Japanese Unexamined Patent Application Publication No.2-289693 (1990) discloses azeotropic compositions comprising dichlorotetrafluoropropane (flon 234) and an aliphatic lower alcohol, such as ethanol. Further, the finish drying using the vapor of isopropyl alcohol (IPA) is disclosed. However, the mixture disclosed in Japanese Unexamined Patent Application Publication No.1-318094 (1989) contains flon 113 as an essential ingredient. Therefore, the reduction of the use of flon 113 is limited. On the other hand, the azeotropic compositions disclosed in Japanese Unexamined Patent Application Publication No.2-289693 (1990) contain flon 234. From the viewpoint of destruction of the ozonosphere, flon 234 is less powerful than flon 113. However, flon 234 cannot completely be free from destruction of the ozonosphere. Further, the use of the vapor of IPA is not practical because it is likely to have influence from water, etc., it is inflammable to thereby have the danger of inflammation, and there is a problem of degrading plastics. Furthermore, EP-A-473795 describes a cleaning method which comprises cleaning an object with a detergent prepared by compounding a basic detergent such as an organosilicon detergent or an isoparaffinic detergent with a detergency improver such as a surfactant or a hydrophilic solvent, rinsing the cleaned object with the basic detergent, and drying it with warm air or steam. It is described therein that the detergent has degreasing and draining properties comparable to those of chlorofluorocarbon detergents and is harmless from the aspect of environmental pollution. EP-A-458969 describes a detergent composition comprising at least one low-molecular polyorganosiloxane selected from among straight-chain polydiorganosiloxanes and cyclic polydiorganosiloxanes. It is described therein that, for use as a water-base detergent, the detergent composition further comprises a polyoxyalkylene containing polyorganosiloxane, a surfactant and water and that it is thus possible to obtain a good dispersion as a watery system free from environmental destruction and environmental pollution and a detergency comparable to that of a fluorocarbon detergent. GB-A-2238793 describes that octa- and/or decamethylcyclosiloxane and/or at least one C 12-14 isoparaffin and/or a dearomatized white spirit with a boiling range of 180 to 210°C is/are used as a solvent for impregnating and/or finishing agents for chemical cleaning, in order to obtain non-toxic solutions, which on drying leave no residues on the cleaned textile or fabrics and do not dissolve as an impurity in perchloroethylene. However, none of EP-A-473795, EP-A-458969 and GB-A-2238793 describes the use of octamethyltrisiloxane of specified purity in high-precision finishing drying of, for example, optical and electronic parts. Summary of The Invention The present invention has been made with a view toward obviating the above problems of the prior art. Therefore, it is an object of the present invention to provide a method for post-cleaning finish drying in which flon destroying the ozonosphere is not used, the influence from water is less, the danger of inflammation at use is less, the cleaned material such as plastics is not corroded and stain and residue are not left after the drying. The foregoing and other objects, features and advantages of the present invention will become apparent from the following detailed description and appended claims. Detailed Description of The Invention The present invention is employed in the finish drying after cleaning of industrial parts, e.g., optical and molded parts composed of glass or plastic, metallic parts, ceramic parts and electronic parts. The present invention is conducted in a final step subsequent to cleaning of industrial parts. Before the final step, the various conventional cleaning treatments, such as defatting of a material to be cleaned by the use of a surfactant or the like, water washing using, for example, demineralized water and alcohol replacement upon water washing, are conducted. Thereafter, the finish drying of the present invention is carried out. The method according to the present invention for finish drying a cleaned material comprises applying to said material an octamethyltrisiloxane having a dodecamethylpentasiloxane content of less than 0.01 % by weight and containing no compounds having volatilities lower than that of dodecamethylpentasiloxane. The terminology "containing no compounds" means that the content of the compounds is on a level such that they are not detected by the customary separating and analyzing means, such as GC (gas chromatography) or LC (liquid chromatography). The degree of volatility is evaluated on the criterion of vapor pressure, taking the latent heat of vaporization into account. From the viewpoint of volatility and danger of inflammation, the use of octamethyltrisiloxane is practical. This low molecular weight siloxane is used because its toxicity to organisms is low, it is chemically stable and has no corrosive effect on plastics, rubbers, metals and glasses and, further, it does not contain halogens, such as chlorine, so that there is no adverse effect on the ozonosphere and high safety is ensured. It may be used in pure form or in the form of a mixture. In the method for finish drying according to this invention, the material cleaned by the cleaning step optionally with water replacement is dipped in the fluid for finish drying, taken out therefrom, and dried by allowing the material to stand still at room temperature, air blasting, vacuum drying. These drying techniques may be employed either individually or in combination. In the above method, a stabilizer or the like may be added. The stabilizer must exhibit high stabilization effect for the employed fluid for finish drying. The preferred stabilizer is one entrained in distillation operation or forming an azeotrope. In the method, use is made of an octamethyltrisiloxane having dodecamethylpentasiloxane removed by distillation, rectification and/or adsorption with active carbon. In the octamethyltrisiloxane the content of dodecamethylpentasiloxane is less than 0.01 % by weight, and the compounds having volatilities lower than that of dodecamethylpentasiloxane are removed. Therefore, there is no occurrence of stain and residue after drying by air blasting or vacuum drying. Table 1 shows results of the following experiment for confirming the effect of minutely contained less volatile components on finished conditions. In the experiment, dodecamethylpentasiloxane was added 0.001 % by weight to each of octamethyltrisiloxane and octamethylcyclotetrasiloxane each having a purity of at least 99.999 % as measured by gas chromatography, which were obtained by a distilling equipment having a theoretical plate number of at least 30. A clean slide glass was dipped in each of the resultant fluids, taken out therefrom and dried by air blasting. The slide glass was subjected to the observation of any stain and residue by a stereo-microscope and the exhalation test in which breath was blown onto the slide glass and any stain and residue were examined by clouding conditions. Further, the same experiment as above was conducted, except that tetradecamethylhexasiloxane was used instead of dodecamethylpentasiloxane. In the evaluation of Table 1, "o" indicates that no stain or residue is detected in both of the observation by a stereo-microscope and the exhalation test, and "x" indicates that stain or residue is detected in at least either of the observation by a stereo-microscope or the exhalation test. Table 1 shows only a summary of the above experiments. From the results, it is found that stain and residue are left either if dodecamethylpentasiloxane is contained in an amount of 0.01 % by weight or more, or if tetradecamethylhexasiloxane less volatile than dodecamethylpentasiloxane is contained irrespective of the minute amount. 0.001 % by weight 0.002 % by weight 0.009 % by weight 0.010 % by weight 0.011 % by weight A B A B A B A B A B Octamethyltrisiloxane o x o x o x x x x x Octamethylcyclotetrasiloxane o x o x o x x x x x Preferred Embodiment of The Invention The present invention will now be described in greater detail with reference to the following Example which should not be construed as limiting the scope of the present invention. Example 1 A glass lens, plastic lenses of polymethyl methacrylate (PMMA) and polycarbonate (PC) and a metallic part of aluminum were cleaned in the following manner. First, each of the above materials to be cleaned was defatted in an alkali saponifier while applying ultrasonic vibration. Re-defatting was conducted in a surfactant while applying ultrasonic vibration. The material was washed in clean water while applying ultrasonic vibration to remove the surfactant. The material was further washed in demineralized water while applying ultrasonic vibration to remove ions and contaminants of clean water, thereby increasing the cleanliness of the material. For draining demineralized water, cleaning in IPA was conducted. The thus cleaned material was dipped in a distillate obtained by distilling octamethyltrisiloxane using a distillation column having a theoretical plate number of at least 30, as a finish drying fluid, taken out, and dried by air blasting. The above finish drying fluid was analyzed by gas chromatography. It was found that the fluid contained 0.009 % of dodecamethylpentasiloxane but did not contain any compound less volatile than dodecamethylpentasiloxane. The gas chromatography was conducted by Gas Chromatograph GC14A (trade name, manufactured by Shimadzu Corp.), and the chromatography conditions were such that the injection temperature, the detection temperature and the temperature elevation rate from 50 to 250 °C were 260 °C, 280 °C and 10 °C/min, respectively. The FID detector and OV-1 capillary column were employed. The finish dried conditions were evaluated by the observation by a stereo-microscope and the exhalation test. No stain and residue were detected, attesting to the performance of desirable finish drying. Attacking Properties The effects of the low molecular weight siloxanes employed in Example 1 on the cleaned plastic materials were evaluated. This evaluation was conducted by first preparing a test piece (5 x 50 x 2 mm) of each of an acrylic resin (PMMA), a glass-filled polycarbonate (PC), a polypropylene resin (PP) and an acrylonitrile-butadiene-styrene resin (ABS), secondly putting the test piece in a glass bottle, thirdly filling the bottle with each of the above low molecular weight siloxanes of Example 1, fourthly allowing the same to stand still for 48 hr under ordinary temperature and humidity conditions, and finally taking out to measure the weight difference and any appearance change. As controls, flon 113 (Daikin Industries, Ltd.) and IPA were tested in the same manner. Results are shown in Table 2. In the Table, "o" indicates a weight difference of less than 1 %, "▴" indicates a weight difference of 1 % or more but no appearance change, and "x" indicates not only a weight difference of 1 % or more but also occurrence of appearance change, such as cracks. PMMA PC PP ABC Example 1 o o o o IPA x x x x Flon 113 o o ▴ o The finish drying of the present invention can be employed in a final step subsequent to cleaning of industrial parts. The finish drying does not corrode the cleaned parts and does not leave stain and residue. Moreover, the finish drying does not use flon so that it does not cause destruction of the ozonosphere. The low molecular weight siloxane is useful as a substitute for flon.

Claims: A method for finish drying a cleaned material, comprising applying to said material an octamethyltrisiloxane having a dodecamethylpentasiloxane content of less than 0.01% by weight and containing no compounds having volatilities lower than that of dodecamethylpentasiloxane. The method according to claim 1, wherein the cleaned material is an industrial part intended to undergo further surface treatment. The method according to claim 2, wherein the cleaned material is an optical part intended to undergo further surface treatment.

Inventors: HIJINO MASAMICHI, KARAKI KAZUHISA, SHIRAI MICHIO, HIJINO, MASAMICHI, KARAKI, KAZUHISA, SHIRAI, MICHIO, HIJINO, MASAMICHI, OLYMPUS NISHIHACHIOJI
Applicants: OLYMPUS OPTICAL CO, OLYMPUS OPTICAL CO., LTD.
Application year: 1994
Main classification: C11D7
IPC codes: F26B5, C11D7